Frank Gehrke, chief of the snow surveys for the Department of Water Resources, carries a snow pack measuring pole as he and Alan Flint, a hydrologist for the United States Geological Service, walk through a snow covered field while conducting the snow pack survey near Echo Summit, Calif., Monday, March 2, 2009. The survey found the snow pack 54 inches deep, with a water content of 25 inches, for an average of 101 percent for this location at this time of the year.(AP Photo/Rich Pedroncelli)

Photo: Rich Pedroncelli, AP

Frank Gehrke, chief of the snow surveys for the Department of Water...

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A heavy downpour during a day mixed with rain and cold temperatures had people scrambling in downtown San Francisco photographed on Monday, March 2, 2009.

The storms pounding the Bay Area and blanketing the Sierra Nevada with snow have brought California back from the brink of the worst drought in state history, but the drenching is not enough to assure adequate water supplies this summer, state water officials said Monday.

The water content of the Sierra Nevada snowpack - the backbone of the state's water supply - is about 80 percent of normal for this time of year, according to measurements of water content at several backcountry spots.

That's a turnaround from a month ago, when the water content measured just 61 percent of normal after the eighth-driest January on record had the state teetering on a the edge of its worst-ever water crisis.

"While the storms that we had in February have certainly improved our circumstances over the first of last month, we still have a long way to go," said Frank Gehrke, chief of snow surveys for the California Department of Water Resources. "Reservoir storage is still way below average, and the likelihood of large-enough storms to have significant recovery drops way off as we move into March."

Elissa Lynn, a meteorologist for the Department of Water Resources, said the water content in the snow would have to be between 120 to 130 percent of normal by April 1 to replenish the state's reservoirs, the largest of which are less than half full.

"That's just the snowpack," Lynn said. "We need to have rainfall in the mountains continuing through the spring, contributing to the total water supply. That's what we had hardly any of last year."

Rain and snow would have to fall virtually every day this month to get back to normal, a highly unlikely scenario, according to Steve Anderson, meteorologist for the National Weather Service.

Couple of feet of snow

He said rain is expected to continue until Thursday. A couple of feet of snow probably will fall above 7,000 feet in the coming days. The weekend and the first half of next week should be dry, and precipitation is expected to be about average for the next two months, he said.

So far, 25 California water agencies have imposed mandatory water restrictions, including the East Bay Municipal Utility District; 66 others - including San Francisco - have voluntary restrictions in place.

Gov. Arnold Schwarzenegger declared a statewide drought emergency last week and urged cities to reduce water use by 20 percent as experts predicted that snowmelt runoff this spring will be just 57 percent of normal. The latest snow survey does not change the dire predictions, Gehrke said Monday.

Still, the measurements of snow depth and water content at Phillips Station, a state measuring site next to the Sierra-at-Tahoe resort, left Gehrke and his colleagues at least moderately optimistic, especially after meager results earlier in the year.

The snowpack was 101 percent of normal at the station, a privately owned cabin off Highway 50. Most of the other surveys came in a bit below normal for an overall average of 80 percent, Gehrke said.

Such measurements are a key indicator of how much water will be available during the dry summer months because as much as 60 percent of the state's water is contained in its snow-covered mountains during the wet season.

When the snow melts in the spring and summer, the water is used to irrigate 775,000 acres of farmland and quench the thirst of California's 36 million people. About one-fourth of the state's power comes from hydroelectric plants that count on heavy mountain runoff.

The measurement at Phillips Station is considered the key measure of water availability in the state. If snowpack is abundant, chances are there won't be a drought.

But nature rules

But nature showed last year that it makes it's own rules. On March 1 the snowpack was 136 percent of normal. Then it stopped snowing, and the state ended up the year with water supplies far below average, Gehrke said. Runoff last year was 58 percent of normal.

January was the Achilles heel of 2009. Lynn said January storms usually douse California, accounting for 18 to 20 percent of the state's annual precipitation. Instead, the month delivered a string of dry, sunny days this year.

The recent storms have left San Francisco at 88 percent of its normal amount of rainfall for this time of year; Oakland is 91 percent of normal. San Jose is just behind, at 86 percent of normal and Santa Rosa is 69 percent of normal.

Two - and maybe three - consecutive dry years come at a difficult time for the state's water supply system. Also hampering water distribution has been aging infrastructure and court-ordered reductions in water pumped through the Sacramento-San Joaquin River Delta - and the state's population continues to grow.

"We can look at this storm and say 'this is good,' but it doesn't mean we can count on it to alleviate the drought conditions," Lynn said. "Last year the rain shut off March 1. We don't want to see that happen again."